Control circuit



April 18, 195o J. E. REILLY 2,504,878

CONTROL CIRCUIT Filed Feb. 24, 1947 WITNESSES:

ATTORNEY lsatented Apr. i8,

UNIT-ED STATES PTENT OFFICE I asusta CONTROL ciRoUrr .lack E. Reilly,Pittsburgh, Pa., assignor to "Westinghouse Electric Corporation, EastPittsburgh,

Pa., a corporation 'of Pennsylvania 'Appleman-'February 24, 1947, serialNo. 730,-s1

11 claims. (ci. S22- 28) This invention relatesto an electronic controlcircuit andiit hasparticular lrelation to a control uior use insuppl-ying ienergylfirorn an alternating voltage source to an @inductiveload, such as the Aiield winding df a "direct current motor or of agenerator. d

In the regulaitivfin ley-"field control of motors andy generators, itisflighly desirable to provide what is known' as neid forcing. Byeldrorcing Iis rnean-t a rapid increasing or decreasing of the :currentthrough "the field-'winding to eiect a frapid change `in`tli"e`freld 'tochange the speed of the armature 'of the r'notoror thefoutput voltage ofthe generator 'as the case might be.

According to the cpefiding application of S.

L. Burgwin, Serial No. 614,945, filed September 17, 11945, the heldwinding f a inotor is energized lfrom an alternating voltage sourcethrough electric valve meansfof' `the*arc-like type, such asthyratron's. Theval've lrne'ansis connected to act as a rectierand'isrendered conductive in each half-perioid'dic thel alternatingsupply voltage to ksupply pulsating iunidirec'tional current throughythe field winding'.v The 'average voltage applied @to the eldIwindingmay be controlled by varying the instant in a half-'period atwhich the 'valve means -|A`loerrne's Y conductive, which instant ishereinafter designated as the ignition point. 'If the yignition 'p At issuddenly advanced, as for regulating pu'rposesna 'corresponding rapidadf Vance inthe `gave voltage applied to the field winding 'ise'ifectedstrengthen theeld rapidly. However, as pointed out in the saidcopendfing application, a delay in the 'ignition point ordinarily wouldnot produce a rapid. weakenf? "ing ci the ld. The ield lwould beweakened but thea'cto'n would be ycomparatively slow be- "cause of theyenergy stored in the eld; The delay `in the 'ignition lpoint tends tospace the puses VVof applied voltage farther apart. However, when itheapplied voltage drops, as at the end of4 a half-period Vof the supplyvoltage, the magnetic energy previously stored in the neld generatesavoltage tending to inai'nt'ain thecurrent through the field ywindingat'i'ts previouslevel.' As a y'recult, the valve means` tendsto'continue to condiict'cu'rrent untill the stored `venergy issubstantiaily dissipated,A which, because of the low iinpedance of thesupply circuit requires a rela- "ti'v'ely long time.

' elsed inf'tnedepending Burgmn applicationan 4 Consequently, Vadelay inthe ignition point does not of itself cause a rapid -'-`wealenin'g"ofthe eld;

arrangementJ in which a capacitor having a rel sister in shunt therewithis connected in parallel circuit relation with (the 'eld winding and iseffective 'to 'cause a rapid rate of change of current through the' eldWinding` when the applied voltage decreases; A rectier is preferablyemployed in connecting the shunt resistor and capacitor in parallel:circuit relation with the field winding, the rectifier being connectedto conduct current only in 'a direction opposite to tha, .finch torl'owby reason of the applied voltage. The rectifier serves to preventoscillations between the ii'eld winding and capacitor.

The arrangement provided by Burgwin op"- erates quite satisfactorilywith most inductive load. However, with certain loads it has been foundthat if the regulation causes the applied voltage to be removed, acapacitor and resistor circuit as disclosed by Burgwin is eiectiveto'take out most ofthe 'energy stored in the held but the remainder isdissipated 'quite slowly. Suche load, for example, is a `field windingfor a generator with additional darnper windings', i. e., shortcircuited turns, on the pole. With such an arrangement, the energy whichis not rapidly removed irom'the 'eld is too great to permita high degreeofiel'd forcing.

It is, accordingly, an 'object of my 'invention to provide a new andimprovedV control system or supplying aninductive'load.

'Another object of kmy invention is to provide a new and improvedcontrol system for'regulating the field of a generator or `motor inwhich the iield winding isfenergize'd lwith pulsating unidirectionalcurrent.

A further object of myinvention is to provide a new and improved-controlsystem for regulating the field of a generator or rn'otor in which theheld winding is yenergized with a unidirectional current derived from an'alternating voltage source through valve; means of the arc-like type.

Still another object of my. invention is to provide a new andiinprovedcontrol vsystem for sup plying an inductivev load withunidirectional cur- 'rent in whicha rapid rate .of change of currentthrough the load is provided. in response to changes fin the yvoltageapplied thereto.

In accordance-with my invention, I provide an arrangement in which arapid change of current through the eld winding is effected when the'applied voltage .is removed by means of a 'l'combination oi a capacitorwitha shunt resistor in paraller'circuitfrelation vwith the eldwind-"ing and means -forapplyingy afreverse voltage to the eldwvinding; Thereverse voltage is preferably of a considerably lower magnitude than theforward applied voltage and is to be applied to the field windingthrough valve means which become conductive when eld winding current ina forward direction drops below a predetermined value. The arrangementis such that when the regulating control voltage causes the appliedfolward voltage to be blocked or removed, the capacitor and resistorproduce an initial rapid de'- crease in iield winding current and whenthe current drops to a predetermined value, the re-A verse voltage isapplied to dissipate the remaining stored energy. Thus a high degree offield forcing may be effected even with damper windings on the pole.

The features of my invention which l consider novel are set forth withmore particularity in the appended claims. The invention itself,however, together with additional objects and advantages thereof may bebetter understood from the following description of a specic embodimentwhen read in connection with the accompanying drawing, in which thesingle figure is a schematic circuit diagram of a generator Voltageregulating system embodying my invention.

, As shown in the drawing, a main supply transformer 3 has a primarywinding 5 energized from alternating Voltage supply lines 'i and 5. Thesecondary winding II of the transformer 3 arranged to supply currentthrough the field winding i3 of a generator I5, with damper windings Italso provided on the pole (not shown). The armature Il of the generatormay be driven by a suitable source of power to generate a voltage acrossa pair of output leads I9 and 2 i.

A pair of main electric discharge valves 23 and 25 of the arc-like type,preferably thyratrons, are interposed between the secondary winding i iof the supply transformer 3 and the field winding I3 of the generatorI5. The anodes 2 and 23 of the main valves 23 and 25 are connected toopposite ends respectively of the secondary winding H. rihe cathodes 3Iand 33 of the main valves 23 and 25 are connected together and through aconductor 35 to one end of the field winding I3, the other end of whichis connected through a resistor 3'I.to an intermediate tap 39 on thesecondary winding II.

The control grids 4I and 43 of the main valves 23 and 25 are connectedthrough individual. grid resistors and 41 to opposite ends of asecondai'y winding 49 of a grid transformer 5l. The center tap 53 on thesecondary windingl i3 of the grid transformer 5I is connected through aresistor 55 and another resistor 51 to the cathodes SI and 33 of themain valves. The primary winding 59 of the grid transformer 5I isenergized from the supply. lines I and 9 through an auxiliarytransformer 6I and a phase-shifting circuit 63. The phase-shiftingcircuit 53 is preferably adjusted so that the alternating voltageappearing across the secondary winding 49 of the grid transformer 5Ibetween the control grid and cathode of each main valve is displaced inby approximately 90 with respect to the anode to cathode voltage.

A direct current biasing voltage is impressed across the resistor 55from a suitable source illustrated as a battery 65. A direct currentvoltage of opposite polarity appears across the resistor' 51 and issupplied from a suitable source of control voltage which is variablewith the output of the generator for regulating purposes.

The resultant grid to cathode voltage for each of the main valves 23 and25 is made up of a .iii

fel;

iii

direct current component of the algebraic sum of the biasing voltage onresistor 55 and the control voltage on resistor 5l and an alternatingvoltage component from transformer 6I. Each main valve, of course, isrendered conductive in a half-period of the supply voltage in which itsanode is positive, at the instant the resultant grid to cathode voltagebecomes more positive than the critical value of the valve. The voltagevalues are arranged so that with an increase in the control voltage theignition point of each valve is advanced and with a decrease in thecontrol voltage the ignition point is delayed.

The main valves 23 and 25 are then rendered conductive alternately insuccessive half-periods of opposite polarity of the alternating supplyvoltage with the ignition point determined by the magnitude of thecontrol voltage. Current then fiows from the secondary winding I i ofthe supply transformer 3 through the main Valves 23 and 25 alternately,the field winding I3 and the resistor 3i to the center tap 39 of thesecondary winding. Thus, pulsating unidirectional current is supplied inwhat might be termed the forward direction through the eld Winding I3,and the average magnitude of that current depends upon the ignitionpoints of the main valves.

While have shown a particular arrangement for delaying or advancing theignition points of the valves, the arrangement is only illustrative andany of the other well-known arrangements for varying the ignition pointswith variation in a control voltage may be employed. By many of theseknown arrangements the ignition points may be varied over substantiallya complete halfperiod.

Io enable a rapid increase in the field Winding current, the voltageacross the secondary winding ii of the supply transformer 3 is arrangedto be several times greater than the normal voltage to be applied to theneld winding I3. Consequently, in supplying rated current through thefield winding I3, the main valves 23 and 25 are not rendered conductiveat the beginning of each corresponding half-period of alternatingvoltage, but their ignition points are delayed vsomewhat so that thedesired lower average voltage is applied. Then, when it is desired tostrengthen the field, i. e., to increase the flux, the ignition pointsmay be rapidly advanced to effect a rapid increase in the field windingcurrent by increasing the average applied voltage.

A capacitor il having a resistor 69 in shunt therewith is connected inparallel circuit relation with Athe field winding I3 through a dioderectifier tube 7l. As described in the aforesaid copending applicationof Burgwin, the capacitor B1 and resistor 69 are arranged to cause arapid rate of change of current through the eld winding I3 when theapplied voltage decreases. With decrease in the instantaneous appliedvoltage, the stored energy in the field generates a voltage across thefield winding tending to maintain the current flow therethrough at itsprevious level. The polarity of this generated voltage is such that therectifier tube 'H becomes conductive. As the capacitor S'l is then in adischarged state, the immediate voltage across the field winding I3 islimited to the arc drop of the rectifier tube 1I. This drop issuniciently small that the conductive one of the main valves 23 and 25becomes nonconductive. The capacitor 6T then charges rapidly todissipate energy previously stored in the field and the shunt resistor69 acts to limit the maximum voltage appearing across the field `windingT3, which may -'be made several times the normal :field voltage. Thus,the previously stored lmagnetic Ienergy is `largely dissipated. However,`as previously indicated, the damper windings on l"the-'field poleIprevent the capacitor 51 and resistor 89 from rapidly dissipating allofthe storedenergy. Consequently, yif the control Vvoltage shouldcausethe main valve to be maintained non-"conductive, as might occur with thecontrol lvoltage provided in accordance with the-generator output in aregulation system, the capacitor t1 yand resistor B9 4causes the current'through the field winding to be vreduced'rapidly to a lower vvalue butsome stored energy remains. To enable rapid dissipation of theremainingstored energy, an auxiliary alternating voitageiis 'provided through van'auxiliary transformer 13 'energized from the supply lines 1 and 9.`auxiliary pair of electric discharge 'valves 15 and 1 1 Aofthe arc-liketype,-pre'ferably thyratrons, lare also provided. The anodes 19 and 8|of the auxiliary valves and 11 are connected to op# :posite ends of thesecondary winding 83 ofthe 'auxiliary transformer 13. The cathodes 84and 85'offtheauxiliary valves 15fand-11 are connected l.together andthrough a resistor 81 to the end of thefleld winding '|3 more remotefrom the cathodes '3| and 33 of the main valves'23 and 25. -A conductor89 completes the circuit from the ends of the Asecondary winding 83l ofthe lauxiliary transformer 13 throughthe field winding I3 'to the'centertap9'l ofthe secondary winding'. The control `grids 93 and 95 oftheauxiliary valves 15 and 11 are connected through correspondingindividual ,grid'resistors91 and 99 to opposite ends ofasecond'arywinding 19| kof asecondv grid transformer |93. The center'tap |05 of thesecondary winding IUI of'the'grid transformer |93 is connected'to anadjustable tapllll on a resistor |09. -oneend of which is connected tothecathodes 94 :and 8-5 of the auxiliary valves 15and 11.

The primary winding of the second 'grid transformerl |03 isalso'arranged to be energized 'from the alternating'voltagesupplylines 1and 9 through the auxiliary transformer 5| and another phase-shiftingcircuit I'I3. `The phaseshifting circuit l I3 is adjusted `sothealternating voltage kappearing across'` the secondary winding '19| ofthesecond grid transformer 4H33 is displacedinphase relative't'o the anodeto cathode voltage of the v'auxiliary valves by va preselected amount.

A direct current 'voltage is produced across the :esistorl09 under'the'control of an amplifier tube 1115. "The'anodelf ofthe amplifiertube ||5-is connected tothe positive'terminal of .a source of directcurrent voltage, illustrated as Ya `battery |19. The cathode |2'I of theamplifier tube 1| I5 1s connected through .a resistor |23 to the kend oftheresistor 31 in the main currentA supply circuit which'is mostremote'from 'the field winding l`3. A lconnection from the end ofthe'resistor 199 remote from the cathodes A83 and 85 of the auxiliaryValves 'I5 and 11 to the negative terminal ofthe voltage source ||9completes the circuit "from the lpositive terminal ofthe source 119through the amplifier tube I5 .and the resistors `l 23,3181- and |99 tothe negative terminal. The control circuit of the amplifier tube |5.maybe-.traced from thecontrol .grid |25 thereof througha'. gridresistor |21 and the resistors 81., |23..andj3`1 to the cathode |2|.lltk follows `that :Lheeurrent through the Yamplifie tube H5 isAvaried-in accordance with'the voltage acrossv the resistor "31 which isa measure of the vforward averageforward current through the fieldwinding I3 and therefore the voltage on resistor 31 drops below apredetermined value, the auxiliary valves 15 and 11 are renderedconductive alter nately in successive half-periods of opposite polarity.When the auxiliary valves 'i5 and 11 becomeconductive, a reverse voltageis applied to the field winding |3 from the auxiliary transformer 13 tocause arapid dissipation of the re- `maining energy stored in the field.While the instantaneous voltage across the resistor 31 drops at the endof each half-period of the supply voltage, the smoothing capacitor |28prevents the amplifier tube from causing the auxiliary valves to'becomeconductive with such drops so that the auxiliary valves becomeconductive only with va drop in average voltage.

The'reverse voltage applied to the eld winding is arranged to beconsiderably less in magnitude than the normal forward applied voltage.Consequently, when the main valves 23 and 25 are again renderedconductive, the forward applied voltage is :suiiicient to supply aforward current of a magnitude `operable through resistor 31 to preventfurther conduction of the auxiliary valves 15 and 11.

It is. apparent v'from the vforegoing description that field forcing maybe readily accomplished. An'increase in the control voltage advances thefiring-point of the main valves 23 and 25 toincrease the voltage appliedto the field winding and increase ythe field. A decrease in the controlvoltage delays the ignition points of the first valves. Because of theaction of the Acapacitor `and resistor, a reduction in the appliedVoltage causes a rapid initial change in current through the fieldwinding, and after the average forward current has dropped below apredetermined value, the reverse voltage is applied through the `secondvalves to continue the rapid decrease in field current.

`While I have shown and described a specific embodiment ofmy invention,I am aware that 'many othermodifications thereof may be made withoutdeparting from the spirit of the invention. '1, therefore, do not wishto be limited to the specific embodiments disclosed.

I claim asmy invention:

1. Apparatus for use with an inductive load comprising means adapted toapply a first voltage of one polarity, the magnitude of which is laterto be re duced,'across said load to produce a current therethrough, acapacitor, a resistor connected in shunt across said capacitor,saidshunt connected capacitor and resistor beingI `connected in parallelcircuit relation with said Vload and effective to cause a rapid initialrate` of `change of current through said `load when the: first voltageis reduced, means adapted to func-` tion as an auxiliary source ofvoltage, and means.

Voperable when said first voltage is reduced below a` ,predeterminedmagnitude to connect said'.

auxiliary source to said load to 'apply a secondi.

annesse voltage thereacross 'of opposite polarity ,to said rst voltage..A.2.Apparatus for use with an inductive load comprising means adapted toapply a irst voltage of one polarity, the magnitude of which is -laterto be reduced, across said load to produce a current therethrough, acapacitor, a resistor connected in shunt across said capaci.- tor.ymeans including a rectifier connecting said shunt connected capacitorand resistor in par.- allel circuit relation with said load, saidrectier being connected to conduct current in a direction opposite tothat which tends to'flow byaD- plication of said first voltage, withsaid capacitor and resistor effective to cause an initial rapid rate ofchange of current through said load when the first voltage is reduced,means adapted'to function as an auxiliaryv source of voltage, and meansoperable when said first voltage is reduced below a predeterminedmagnitude to conneet said auxiliary source to said load to apply asecond voltage thereacross of opposite polarity to said first voltage.

3. Apparatus for use with an inductive load comprising means adapted tovfunction as a source of first voltage of one polarity conductivelyconnected across said load to produce current in one directiontherethrough, control means for varying said first voltage, meansadapted to function as an auxiliary source of voltage, and meansresponsive to current between said main source and load and effectivewhile that current in said one direction is less than a predeterminedvalue to connect said auxiliary source to said load to apply a secondvoltage thereacross of opposite polarity to said first voltage. f

4. Apparatus for use with an inductive load comprising means adapted tofunction as a source of rst voltage of one polarity conductivelyconnected across said load to produce a current in one directiontherethrough, control means for varying said first voltage, a capacitor,a resistor connected in shunt across said capacitor, said shuntconnected capacitor and resistor being connected in parallel circuitrelation with said load and effective to cause an initial rapid rate ofchange of current"l through said load when the first voltage appliedacross said load is reduced, means adapted to function as an auxiliarysource of voltage, and means responsive to current between said mainsource and load and eiective while that current in said one direction isless than a predetermined value capacitor, means including a-rectierconnecting said shunt connected capacitor and resistor in parallelcircuit relation with said loa-d, said rectifier being connected toconduct current only in a direction opposite to that which tends to flowby application of said first voltage, with said capacitor and resistoreffective to cause an initial rapid rate of change oi current throughsaid load when the first voltage applied acrossvsaid load is reduced,means adapted to function as an auxiliary source of voltage, and meansresponsive to currentbetween said 'main source and loadandeffective-while that current in said one direction is less than apredetermined value-to connect said auxiliary source to said load toapply a second voltage thereacross of opposite polarity to said rstvoltage.

l(i. Apparatus for use with an inductive load comprising means adaptedto function as a main source of alternating voltage, means includingfirst valve means of the arc-like type connecting said main source tosaid load to supply current therethrough in one direction under thecontrol of said first valve means, control means to render saidfirstvalve means conductive in half-periods of said main source, said controlmeans being variable to determine the instant in a half-period at whichthe first valve means becomes conductive to vary the average voltageapplied to said load from said main source, means adapted to function asan auxiliary source of voltage, means including second valve meansconnecting said auxiliary source to-said load to supply currenttherethrough in theopposite direction under the control of said secondvalve means, and means responsive to current between said main sourceand load and effective While the average of that current in said onedirection is below a predetermined value to cause said second valvemeans to be conductive.

7; Apparatus for use with an inductive vload comprising means adapted tofunction as a main source of alternating voltage, meansincluding firstvalve means of the arc-like type connecting said main source to saidload to supply current therethrough in one direction under the controlof said rst valve means, control means to render said first valve meansconductive in half-periods of said main source, said control means beingvariable to determine the instant in a half-.period at which the firstvalve means becomes conductive to vary the average voltage applied tosaid load from said main source, a capacitor, a resistor connected inshunt across said capacitor, said shunt connected capacitor and resistorbeing connected in parallel circuit relation with said load andeffective to cause an initial rapid rate of change of current throughthe load when the instantaneous voltage applied to the load from saidmain source is reduced, means adapted to function as an auxiliary sourceof voltage, means in cluding second valvev means connecting saidauxiliary source to said load to supply current therethrough in theopposite direction under the clontrol of said second valve means, andmeansresponsive to current between said main source and load andeffective while the average of that curof said rst valve means, controlmeans to Arender said first valve meansconductive in half-periods of,said main source, said control means lbeing variable to determine theinstant in a half-period at ,which the first valve means becomesconductive to vary the average voltage appliedto said .load from saidmain source, a capacitor, a resistor connected in shunt across saidcapacitor, means including a rectifier connecting said shunt connectedcapacitor and resistor in parallel cir'- cuit relation with said loadwith the rectier connected to conduct current only in a directionopposite to that which tends to ow by application of the iirst voltage,said capacitor and resistor being effective to cause an initial rapidrate oi change oi current through said load when the instantaneousvoltage applied to the load from said main Source is reduced, meansadapted to function as an auxiliary source of voltage, means includingsecond valve means connecting said auxiliary source to said load tosupply current therethrough in the opposite direction Linder the controloi said second valve means, and means responsive to current between saidmain source and load and effective while the average of that current insaid one direction is below a predetermined value to cause said secondvalve means to be conductive.

9. Apparatus for use with an inductive load comprising means adapted tofunction as a main source oi alternating voltage, circuit meansincluding first valve means or" the arc-like type connecting said mainsource to said load to supply current therethrough in one directionunder the control oi said first valve means, control means to rendersaid rst valve conductive in half-periods oi said main source, saidcontrol means being variable to determine the instant in a half-periodat which the nrst valve means becomes conductive to vary the averagevoltage applied to said load from said main source, a capacitor, aresistor connected in shunt across said capacitor, means including arectifier connecting said shunt connected capacitor and resistor inparallel circuit relation with said load with the rectiiier connected toconduct current only in a direction opposite to that which tends to iiowby application of the first voltage, said capacitor and resistor beingeffective to cause initial rapid rate of change of current through saidload when the instantaneous voltage applied to the load from said mainsource is reduced, means adapted to function as an auxiliary source oialternating voltage, means including second Valve means of the arc-liketype connecting said auxiliary source to said load to supply currenttherethrough in the opposite direction under the control oi said secondvalve means, said circuit means including a second resistor interposedbetween said main source and load whereby a Voltage is developedthereacross proportional to the current flowing between said main sourceand load, and means responsive to the voltage across Said secondresistor for rendering said second valve means conductive in eachhalf-period of said auxiliary source voltage While the average voltageacross said second resistor is below a predetermined value.

10. Apparatus for use in regulating a rotating electric machine having afield winding and damper windings on the pole thereof, comprising meansadapted to function as a source of first voltage of one polarityconductively connected across said eld winding to produce current in onedirection therethrough, control means responsive to the output of saidmachine for Varying said first voltage accordingly to regulate themachine, a capacitor, a resistor connected in shunt across saidcapacitor, said shunt connected capacitor and resistor being connectedin parallel circuit relation with said eld winding and effective tocause an initial rapid rate of change of current through the fieldwinding when the iirst voltage is reduced, means adapted to function asan auxiliary source of second voltage, controllable circuit meansconnecting said auxiliary source to said field winding in opposition tosaid polarity, and control means responsive to current between saidsource of rst voltage and load for controlling said circuit means toapply said second voltage to said eld winding only when the average ofsaid current in said one direction is more than a predetermined value.

l'l. Apparatus for use in regulating a rotating electric machine havinga eld winding and damper windings on the pole thereof, comprising meansadapted to function as a source of iirst voltage of one polarityconductively connected across said iield winding to produce current inone direction therethrough, control means responsive to the output ofsaid machine for varying said iirst voltage accordingly to regulate themachine, a capacitor, a resistor connected in shunt across saidcapacitor, means including a rectier connecting said shunt connectedcapacitor and resistor across said held winding with said rectifierpoled to conduct current only in a direction opposite to that of thecurrent which tends to iiow by application of said first voltage, withsaid capacitor and resistor eilective to cause an initial rapid rate ofchange of current through the eld winding when the first Voltage isreduced, means adapted to function as an auxiliary source of voltage,and circuit means responsive to current between said main source andload and effective while the average of that current in said onedirection is less than a predetermined value to connect said auxiliarysource to said eld winding to apply a second voltage thereacross ofopposite polarity to said iirst voltage.

JACK E. REILLY.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,913,952 Powell l June 13, 19332,031,509 Seeley Feb. 18, 1937 2,220,755 Edwards Nov. 5, 1940

